Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and systems for generating and/or measuring electromagnetic (EM) fields and, more particularly, to mechanisms and techniques for enhancing detection of near surface, lateral or vertical conductive targets.
Discussion of the Background
EM surveying is a method of geophysical exploration to determine the properties of a portion of the earth's subsurface, information that is especially helpful in the oil and gas industry and the mining industry. EM surveys may be based on a controlled source that generates a primary EM field which carries EM energy into the earth, which induces eddy currents in the earth. The eddy currents generate a secondary EM field or ground response. By measuring the secondary field with an EM receiver, it is possible to estimate the depth and/or composition of the subsurface features. These features may be associated with subterranean hydrocarbon deposits.
A schematic airborne EM survey system 100 generally includes, as illustrated in FIG. 1, a transmitter 102 for generating the primary EM field 104 that is directed toward the earth. When primary EM field 104 enters the ground 108, it induces eddy currents 106 inside layers 116 and 118 of the earth. These eddy currents 106 generate a secondary electromagnetic field or ground response 110. An EM receiver 112 then measures the response 110 of the ground. Transmitter 102 and receiver 112 may be connected to an aircraft 114 so that a large area of the ground is swept. Receiver 112 may be located concentric and/or coplanar with transmitter 102. A second receiver 113 may also be added.
However, the existing EM surveying systems are not sensitive to near surface formation detection as the signals usually associated with such formation are buried in either ambient or geologic noise. Thus, there is a need to have a new system that is capable of measuring signals associated with near surface formation detection.